Certain linearly vibrating vibration gyroscopes are believed to be conventional. In these rotation rate sensors, parts of the sensor structure are actively put into a vibration (primary vibration) in one direction, e.g., in a first axis (the x axis). In the case of an external rotation rate about a singular sensitive axis, Coriolis forces are exerted on the vibrating parts. These Coriolis forces (that are changeable periodically at the frequency of the primary vibration) effect vibrations of parts of the sensor structure (secondary vibration) in a second direction or second axis (the y axis) which is oriented perpendicularly to the x axis. A detection device is mounted on the sensor structure, which detects the secondary vibration (Coriolis measuring effect).
In the construction of the rotation rate sensors, in the design, by the choice of suitable symmetries, an excellent Cartesian coordinate system K=(x, y) is specified for the primary and the secondary vibration within the substrate plane. The mass distributions and the spring distributions are arranged such that the main axis systems of the mass sensors and the spring stiffness or spring constant sensors for the primary and the secondary vibrations agree exactly with K.
Furthermore, in the execution of the detection device, care is taken that, because of the operation of the sensors in the primary vibration (without external rotation rate) no signals are created at the detection device for the Coriolis effect. For this purpose, the detection device is arranged such that its designated coordinate system KD also agrees with the coordinate system of the mechanics K, that means, then, that KD=(x, y) also applies.
Consequently, in such ideal rotation rate sensors no overcoupling of the primary vibration into the detection device is created. Such an overcoupling that occurs in real rotation rate sensors is called quadrature. Consequently, quadrature signals are signals at the detection device, for the Coriolis effect, which are present even without relative motion of the sensor with respect to an external inertial system, the sensor being operated in its primary vibration.
The quadrature leads to periodic signals modulated by the frequency of the primary vibration, at the detection device, for the Coriolis effect. The reason for the appearance of the quadrature signals is that the coordinate system of the sensor element mechanics K=(x, y) does not coincide with the coordinate system of the detection device KD=(x′, y′), but rather, the two systems are slightly rotated with respect to each other by an angle.
Typical causes for these generally slight rotations are, for example, asymmetries in the sensor structure caused by imperfections in the manufacturing process. These may manifest themselves by asymmetric mass distributions or even asymmetric spring stiffnesses. As a result, the main axis systems of the mass tensors and the spring stiffness tensors no longer agree with KD.
Quadrature interference signals in the case of rotation rate sensors caused by imperfections in the manufacturing process are known, and are encountered in rotation rate sensors in the most varied technologies. In this context, different methods are believed to be conventional for reducing these interference signals.
A first conventional method for suppressing the quadrature signals utilizes the different phase position of rotation rate signals and quadrature signals. The Coriolis force is proportional to the speed of the primary vibration, as opposed to which the quadrature is created proportional to the deflection of the primary vibration. Thus, there exists a phase shift of essentially 90° between the rotation rate signal and the quadrature signal. At the detection device, quadrature signals and rotation rate signals are detected as signals that are amplitude modulated by the frequency of the primary vibration. By the method of synchronous modulation or phase-sensitive amplification, as described, for example, in German Published Patent Application No. 197 26 006 and also in U.S. Pat. No. 5,672,949, the signals are first of all able to be demodulated again into the base band. In addition, the quadrature signal may be suppressed by a suitable selection of the phase position of the reference signal for the demodulation. In this method, the quadrature signal is not influenced in the sensor element itself. Furthermore, the quadrature signal also has to pass the primary signal conversion paths at the detection device, it can only be suppressed electronically relatively late in the signal path. In the case of quadrature signals that are large compared to the rotation rate range, this means drastically increased demands on the dynamic range of the first signal conversion steps, and often leads to increased sensor noise.
A second conventional method for reducing the quadrature signal is the physical balancing out of the mechanical sensor structures. In this instance, in contrast to the first method, the cause of the quadrature is directly removed by reworking the sensor elements, so that no quadrature signals occur at the detection device.
According to an additional generally conventional method, an electronic quadrature compensation is performed in capacitive micromechanical rotation rate sensors. In this connection, the suppression of the quadrature signal is achieved at the detection device for the Coriolis effect by the purposeful injection of an electrical signal into the electronic converter unit. In so doing, the magnitude of the signal is selected such that the signal generated by the quadrature exactly compensates at the detection device.
In U.S. Pat. No. 6,067,858, an additional conventional method is described for the electronic quadrature compensation in capacitive micromechanical rotation rate sensors. Different electrical potentials are applied between movable comb fingers and stationary electrodes.
In German Published Patent Application No. 102 37 411 it is described how, based on the targeted intervention of forces varying periodically with time, a reduction or avoidance of quadrature signals is achieved. To do this, electrostatic forces varying in time (dynamic) are exerted on the sensor structure because of electrode structures (compensation structures) mounted at suitable parts of the sensor structure, by the purposeful application of external electrical direct voltages.